If you are in IMC, anybody within 1000' of you should be either on the ground or on the radio on the appropriate frequency.
otherwise, they're operating illegally.
But there can be others in VMC, more than 1,000' below the cloud base of the IMC in which you're operating, and not required to have a radio, can there not? I thought the scenario was practising approaches, during which you may pop out of that IMC? We may at crossed purposes.
[AOTW: Leadsled and Lead Balloon are not one and the same.]